1. Field of the Invention
This invention relates to an image-forming apparatus, such as a copying machine or a printer, which employs an electrophotographic process.
2. Related Background Art
Printers employing an electrophotographic process are conventionally constructed as shown in FIG. 1.
A paper feed cassette 2 is set at the lower part of the main body 1 of a printer, and sheet material P is loaded into a sheet loading board 201. With regard to the sheet materials P, a pick-up roller 202 is driven by a main motor (not shown) and rotated in the direction of an arrow A, whereby the sheet material P is sheet-by-sheet delivered to twin paper feed rollers 203 consisting of a paper feed roller 203a and a retard roller 203. The uppermost sheet material P is separated then fed to first twin delivery rollers 301 consisting of a first delivery roller 301a and a support roller 301b. The sheet material P delivered to the first twin delivery rollers 301 is delivered to second twin delivery rollers 302 consisting of a second delivery roller 302a and a support roller 302b, and is further delivered to a transfer zone formed by a transfer photosensitive member 401 and a transfer roller 402 which are held in a cartridge 4. At the transfer zone, image signals processed by a controller (not shown) are written as an electrostatic latent image on the transfer photosensitive member 401 by means of a scanner 5. The electrostatic latent image is developed with a toner, and thereafter the developed image is transferred to the sheet material P as an unfixed image.
The sheet material P to which the unfixed image has been transferred is delivered through a transport guide 403 to a fixing assembly 6. In the fixing assembly 6, a heater unit 601 consists of a ceramic heater 601a, a fixing film 601b, a film guide 601c and a stay 601d. Upon applying an alternating current, the ceramic heater 601a heats the fixing film 601b, and a pressure roller 602 applies a stated pressure, thus the unfixed image on the sheet material P delivered there is fixed. The sheet material P having the image thus fixed is delivered to first twin paper-output rollers 603 consisting of a first paper-output roller 603a and a paper-output support roller 603b. 
In the case of double-side printing, a flap 14 moves upward to the position shown by dotted lines, and the sheet material P to which the unfixed image has been fixed is delivered to twin reversible rollers 801 of a double-side unit 8; the rollers 801 consisting of an reversible roller 801a which rotates in the direction of an arrow D and an reversible support roller 801b. Then, the sheet material P is sent to a delivery path 807. The rotation of the reversible roller 801 is switched to the direction of an arrow E, so that the sheet material P delivered to the delivery path 807 by a predetermined length is delivered to a delivery path 808, and then sent on to first twin double-side-printing delivery rollers 803 consisting of a first double-side-printing delivery roller 803a and a support roller 803b and to second twin double-side-printing delivery rollers 804 consisting of a second double-side-printing delivery roller 804a and a support roller 804b. 
Thereafter, at given timing, the sheet material P is again delivered to the first twin delivery rollers 301 and the second twin delivery rollers 302, and, at the transfer zone formed by the transfer photosensitive member 401 and the transfer roller 402, an unfixed image is transferred to the second-side surface which is the back of the first-side surface, in like manner on the first-side. surface.
The sheet material P to which the unfixed image on the second-side surface has been transferred is again delivered through the transport guide 403 to the fixing assembly 6, where the unfixed image on the second-side surface is fixed, and the sheet material P having the having the image thus fixed on the second-side surface is delivered to the first twin paper-output rollers 603. After the fixing on the second-side surface, the flap 14 stands on the position shown by solid lines, and the sheet material P is delivered to second twin paper-output rollers 701 consisting of a second paper-output roller 701a and a paper-output support roller 701b, and discharged on a face-down tray 702.
A detailed construction of the fixing assembly 6 is shown in FIG. 2.
On the downstream side of the heater unit 601 and pressure roller 602, provided are a lower guide 609 which guides the sheet material P to the first twin paper-output rollers 603 and an upper guide 612. Materials for the lower guide 609 and upper guide 612 are formed of a polymer composition (Type P) shown in Table 1.
Numerical values of the triboelectric voltage, surface resistivity and contact angle water repellency of the polymer composition (Type P) are shown in Table 2.
Remainder ingredients: glass fiber, an antioxidant, a flame retardant, and an auxiliary flame retardant.
Triboelectric voltage is a value measured by the method prescribed in JIS L1094B.
However, the above prior art has disadvantages as stated below.
After the fixing on the fist-side surface, the toner image heat-fixed by the heater unit 601 and pressure roller 602 may adhere to the upper guide 12 before it solidifies completely onto the sheet material. Since the toner is very cohesive to each other, it may grow or accumulate gradually on the upper guide 612 every time the sheet material is delivered, so that the image on the sheet material delivered later may be scraped with the toner having accumulated on the upper guide, or the sheet material may run against the toner having accumulated on the same to cause a paper jam.
When the toner image is fixed on the second-side surface, the first-side surface is also heated because of the fixing on the second-side surface. Hence, the toner may likewise accumulate on the lower guide 609, and in addition image scraping and paper jamming may likewise occur as a result of the accumulation of the toner.
As a means for preventing the above-mentioned problems, a method is available in which the guide is coated on its surface with an ultraviolet-curing resin so that the toner does not adhere to the guide; the resin containing fluorine resin (such as PFA or ETFE) particles dispersed therein (hereinafter xe2x80x9cUV coatingxe2x80x9d). This UV coating provides a contact angle of 100xc2x0 or above, at which water repellency is exhibited, so that the toner does not adhere to the delivery guide surface.
However, a problem in the UV coating is that the UV coating itself results in a very high cost because the guide is produced through many steps of setting a guide member to a jig, coating it with a coating material, curing coatings with ultraviolet rays, controlling the coating layer thickness and so forth when the guide member is coated.
The UV coating has another problem that the coating film formed may wear gradually as a result of its contact friction with the sheet materials. To the part from which the UV-coating film has worn away, the toner tends to adhere, as in the case of the problems in the prior art. Once it has adhered, since the toner is very cohesive to each other, it may accumulate gradually on the part where the material (PET) of the guide member is laid bare, so that the leading end of the sheet material may be caught there to cause a paper jam.
As another problem, when the UV coating is applied on the guide member, an adhesive solvent is used to make it easy that the ultraviolet-curing resin to be coated, containing fluorine resin (such as PFA or ETFE) particles dispersed therein, adheres to the guide member. Hence, depending on materials (materials containing PC) for the guide member, the resin material may be attacked by the adhesive solvent to cause cracks in the guide member.
Also in view of recycling, there is such a problem that the resin provided with the UV coating is difficult to reuse.
Accordingly, an object of the present invention is especially to provide an image-forming apparatus in which its delivery guide member can be free from any deterioration in antistatic properties even as a result of its contact friction with the sheet materials and hence the toner does not accumulate on the delivery guide member to prevent any image scrape and paper jam from being caused by the accumulation of toner.
The present invention provides an image-forming apparatus in which, using a photosensitive member and a toner, an unfixed image of the toner is formed on a transfer medium and the unfixed image on the transfer medium is fixed by a heat-and-pressure fixing means, wherein;
a delivery guide member which guides the delivery of the transfer medium, positioned in the vicinity of the heat-and-pressure fixing means, has a value of triboelectric voltage not greater than 500 V as measured by the triboelectric voltage measuring method according to JIS L1094B.
In the present invention, the triboelectric voltage of the delivery guide member which is positioned in the vicinity of a heat-and-pressure fixing means of an image-forming apparatus and delivers the transfer medium is controlled. Thus, the unfixed toner image transferred to the transfer medium is kept from adhering to and accumulating on the delivery guide member, so that good images can stably be obtained in the image-forming apparatus without requiring any complicated process for producing the guide member and applying any special treatment that makes its reuse difficult.